1. Field of the Invention
The invention pertains generally to the art of transport refrigeration systems and in particular to an arrangement for detecting a loss of refrigerant charge in such a system.
Transport refrigeration units are used to keep the served space in which commodities are shipped at or close to a given temperature through the use of a refrigeration system which is adapted to provide either heating or cooling since different kinds of commodities may require vastly different temperatures. Frequently, in the shipment of such commodities, the refrigerated trailer or other served space may be unattended for periods of up to a number of days, such as when a truck stops overnight at a truck stop, or a trailer is left at a freight terminal over a weekend, or a "piggyback" trailer spends several days unattended on the railroad flat car of a cross-country train. If there is a loss of refrigerant due to system leakage while the refrigeration unit is unattended, the continued operation of the compressor for more than a limited period, such as a half hour to one hour may result in compressor failure. The failure, of course, is due to loss of oil in the compressor rather than the loss of the refrigerant itself.
While in some applications a suction line low-pressure cut-out switch can protect against compressor destruction through loss of refrigerant charge, such a safeguard is not practical if the system must operate throughout a wide range of evaporator temperatures and suction pressures, as is the case with transport refrigeration units.
Accordingly, it is considered desirable to have some arrangement for determining that a given refrigerant charge has been lost in a transport refrigeration system and to provide means for generating at least a warning signal in accordance with a predetermined loss.
It is the aim of this invention to provide such an arrangement for a transport refrigeration system.